One stunning piece of news in tonight's Science News presents the results of a study aimed at determining the effects of lead upon IQ at levels below those deemed "safe". When the studies of lead showed that relatively high lead levels in the blood were associated with reduced IQ scores, medical advisory panels set a level of 60 micrograms per deciliter as safe (1960-1970). The federal Center for Disease Control lowered that level to 38 mcg./dl from 1970 to 1985, then to 25 mcg/dl from 1985 t0 1991, and to 10 mcg/dl thereafter. Now this later study has shown that children with bloodstream lead levels that were less than 1 micrograms per deciliter scored 11 points of IQ higher on an IQ test than matched children with lead levels below 10 micrograms/deciliter. 11 points of IQ is equivalent to 37 years of Flynn Effect. The researchers have concluded that no level of lead is safe. Another study says, "As more data become available, the definition of lead toxicity level will likely continue to be lowered." Serum lead levels of 10 mcg/dl are associated with reduced IQ, reduced stature, hearing loss, and hypertension. "A 1990 follow-up report of children with elevated lead levels in their teeth noted a sevenfold increase in the odds of failure to graduate from high school, lower class standing, greater absenteeism, more reading disabilities, and deficits in vocabulary, fine motor skills, reaction time, and hand-eye coordination 11 years later." "Until fairly recently, nearly one child in six was affected by lead poisoning at least to some degree, according to U. S. Public Health Service estimates."
According to the CDC's estimate, every 10-microgram increase in lead levels may cause an irreversible drop of 1 to 3 IQ points.
The above quotations are taken from "Case Studies in Environmental Medicine: Lead Toxicity", U.S. Department of Health and Human Services, Public Health Service, Agency for Toxic Substances and Disease Registry... not exactly, a rabid, rabble-rousing source.
What role do declining lead levels play in the Flynn Effect? The Romans used lead (plumbum) pipes for their plumbing. It's thought that the decline and fall of Rome may have been the result of the lead levels in their drinking water. Lead was used in dentures in George Washington's day. It is frequently used in pewter. It was a constituent of gasoline (in the form of tetraethyl lead) and of various paints (Dutchboy White Lead) for decades.It has always been a component of the solder used to bond copper plumbing. It's still the principal ingredient of storage batteries. Could the Flynn Effect be a result of gradually declining levels of lead? And what about other metals in our environment? What about mercury? How about mercury amalgams in the fillings in our teeth? "Prior to 1990, paints contained mercury as an anti-mildew agent. In medicine, mercury is used in dental amalgams and various antiseptic agents." "Patients with dental amalgam fillings have slightly elevated levels in their urine, but these findings have not correlated with any systemic disease." In the meantime, there's study after study and warning after warning showing that the mercury in your fillings is leaching into your body. The dental industry's stance with respect to mercury in fillings reminds me of the tobacco industry's 1970's stance regarding the link between smoking and lung cancer, or the butter, beef and egg interests' 1970's stance with respect to heart disease.
There are other toxic heavy metals, including arsenic, cadmium, and nickel. (Everything used to be cadmium-plated or nickel-plated.) It will be interesting to see what will happen as these metals are eliminated from our environments and ourselves.
It would appear to me that these toxic metals could possibly have played some role in depressing IQ's in the past. The question is: how much?